Due to the lack of fixed landmarks and pathways marine navigation, positioning and hazard avoidance has historically been a problem of great importance. Throughout history, may devices and methods have been utilized to provide a mariner with accurate information concerning his location as well as the location of moving and stationary surroundings. Historically, mariners have used a variety of methods for navigation, including visual observation of known landmarks (referred to as piloting), dead reckoning and celestial observation. Modern developments made electronic navigation possible as well. In electronic navigation, a ship's position is determined with the aid of devices such as radar. These instruments variously make use of the directional properties of radio waves or differences in the times of arrival of radio signals sent simultaneously from different locations or occasionally of the difference in speed between radio waves and sound waves. Today, electronic devices such as radar are widely used in navigation. Most recently, a satellite based system designed, financed, deployed and operated by the U.S. Department of Defense, called Global Positioning System, has been providing continuous worldwide coverage adequate for determining latitude and longitude to within about 30 feet (10 meters), and in many places altitude with the same accuracy. The service is available all over the globe 24 hours a day and free of any charge. The use of the Global Positioning System (GPS) coupled with computer technology, provides a user with positions relative to fixed locations, such as roads on land or the coastline on water to be displayed on an electronic map with a high degree of accuracy. However, even with the use of modem GPS based systems, a mariner still must rely on visual contact or radar to know the position of his vessel relative to other vessels or other moving objects on the water.
It would therefore be desirable to have a GPS based system that can provide a plurality of users with precise positional data regarding their own vessel as well as other similarly equipped vessels as well as providing navigational data for finding a course from one location to another.